Speaker
Description
The GBAR collaboration (Gravitational Behaviour of Antihydrogen at Rest) at CERN [1] aims to test the equivalence principle with antimatter by measuring the gravitational acceleration experienced by antihydrogen $\overline{\textrm{H}}$ prepared at rest. This experiment involves the use of laser-cooled $^9\textrm{Be}^+$ ions and a sympathetically cooled $\overline{\textrm{H}}^+$ ion.
The experiment relies in part on the efficient cooling of the $\overline{\textrm{H}}^+$ antimatter ion composed of an antiproton and two positrons. The principle of this cooling step, proposed by Jochen Walz and Theodor W. Hänsch in 2004 [2] consists in capturing an antihydrogen ion launched with an energy of about 1 eV. Then, starting a sympathetic cooling process using a crystal of about a thousand $^9\textrm{Be}^+$ ions confined in an ion trap. After this step, the $\overline{\textrm{H}}^+$ ion temperature is expected to reach a few mK. This first cooling stage is preliminary to Raman sideband cooling (this topic will not be covered in the presentation). Ultimately, the goal is to measure the gravitational acceleration experienced by antimatter with an uncertainty of approximately 1 %.
Our experiment aims to simulate the sympathetic cooling stage of the GBAR project. It consists in launching, with a controlled energy, a single $^9\textrm{Be}^+$ ion into a cloud of laser-cooled $^{88}\textrm{Sr}^+$ ions and studying the sympathetic cooling process. These two species are particularly well suited for this experimental simulation, as their mass ratio is very close to that of the ($\overline{\textrm{H}}^+$, $^9\textrm{Be}^+$) pair, making the sympathetic cooling dynamics in both systems nearly identical. In particular, we aim to characterize the cooling times as a function of the initial energy.
This presentation will focus on our ability to launch a single ion with a controlled energy from an initial to a final potential well in a linear surface Paul trap. I will detail the Doppler recooling technique [3] used to characterize the ion's initial energy. This characterization relies on analyzing the fluorescence rate dynamics as the ion evolves from an initial hot state to a final cold state. Since this technique strongly depends on the scattering rate of the ion, I will also present a recent study [4] providing a quantitative understanding of the scattering rate for atomic ions with metastable states, such as $^{88}\textrm{Sr}^+$.
[1] P. Perez and Y. Sacquin. The gbar experiment: gravitational behaviour of antihydrogen at rest, Classical and Quantum Gravity 29(18) 184008, 2012.
[2] Jochen Walz and Theodor W. Hänsch. A Proposal to Measure Antimatter Gravity Using Ultracold Antihydrogen Atoms, General Relativity and Gravitation 36(3) 561–570, 2004.
[3] J. H. Wesenberg, R. J. Epstein, D. Leibfried, R. B. Blakestad, J. Britton, J. P. Home, W. M. Itano, J. D. Jost, E. Knill, C. Langer, R. Ozeri, S. Seidelin, and D. J. Wineland. Fluorescence during doppler cooling of a single trapped atom, Phys. Rev. A 76 053416, 2007.
[4] V. Martimort, S. Guesne, D. Drapier, V. Tugayé, L. Gros-Desormeaux, V. Cambier, A. Douillet, L. Guidoni and J-P. Likforman. Incoherent repumping scheme in the $^{88}\textrm{Sr}^+$ five-level manifold, arXiv preprint arXiv :2512.08710, Dec 2025.
| Academic level | PhD student |
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